The invention relates to an installation for continuously sterilizing food products contained in flexible packages.
Sterilizing food products contained in flexible packages requires the packages to be placed in an enclosure under pressure during the sterilization stage and during the cooling stage in order to prevent the packages bursting under the effect of the internal pressure that is generated by the rise in temperature during the treatment. This is particularly true when the product to be sterilized is contained in a flexible bag. When the products are contained in semirigid trays, U.S. Pat. No. 5,245,916 proposes a tray support which holds the edges of a tray and its capsule against internal pressure forces, and said container support is handled as though it were a rigid container, jar, or metal can. Such tray supports increase the cost of the installation and of handling, and they cannot be used for protecting flexible bags.
As a general rule, food products are sterilized continuously in tower-type sterilizers in which the products travel along up and down paths, with the pressure inside such towers increasing between end towers and a middle tower referred to as the sterilizing tower. The change in pressure between two successive towers is obtained by means of a difference in water level in the up portion of one tower and the down portion of the other tower.
Those sterilizers are adapted to products contained in rigid packages, but they are not adapted to flexible packages such as bags since such packages are subjected to large changes of pressure on being immersed in water columns of great height.
Belgian patent BE 901 695 describes treatment apparatus comprising at least one moving carriage containing a plurality of packets of products to be treated and moving around a closed loop having a plurality of successive treatment stations: a heat treatment station comprising a pressurizing chamber, a sterilizing chamber, and a decompression chamber; a cooling station for cooling the carriage and the products; a carriage-unloading station; and a carriage-loading station.
The carriage coming from the sterilizing chamber is delivered to the decompression chamber which is in the form of a lock receiving hot water at the pressure of the sterilizing chamber. The carriage remains in the decompression chamber for a short length of time only. The hot water is removed and replaced with cold water, after which the decompression chamber is put to atmospheric pressure, and the carriage together with its still-hot products is taken away to the cooling station.
The apparatus described in BE 901 695 thus enables bags to be treated during the temperature rise stage, providing the pressure which exists inside the sterilizing chamber is sufficient to counter the pressure that exists inside the bag due to the temperature rise, but at the outlet from the decompression chamber, because the products are still hot and are subjected to atmospheric pressure, that apparatus is unsuitable for treating bags since a plurality of bags might burst or become damaged at the outlet of the decompression chamber.
In BE 901 695, the carriages are moved through the locks and the sterilizing chamber by means of a wormscrew which co-operates with a stud formed on a side wall of the carriage. In addition to the wear which is inevitable in a hot atmosphere, that disposition also requires leakproof bearings for supporting the wormscrew where it passes through the end walls of the installation.
U.S. Pat. No. 4,169,408 and U.S. Pat. No. 4,646,629 disclose installations for continuously sterilizing products contained in packages placed on carriages, in which the carriages are driven stepwise through the sterilizing chamber by means of a long piston rod carrying a plurality of pusher fingers. Those installations likewise require means for sealing the bearings provided through the end walls of the sterilizing chamber and through which the piston rods slide. In addition, the pusher fingers are difficult to access during maintenance.operations.
The object of the invention is to propose a continuous sterilizing installation in which the sealing problems of the prior art are eliminated.
The invention thus provides an installation for continuously sterilizing products contained in packages, in particular flexible packages, the installation comprising:
a plurality of moving carriages suitable for moving one after another around a closed path comprising a loading station in which a batch of packages to be treated is loaded onto a carriage by loading means, and an unloading station in which a batch of treated packages is unloaded from a carriage by unloading means, said carriages passing successively between the loading station and the unloading station via:
an inlet lock suitable for receiving carriages loaded with respective batches of packages for treatment from the loading station at a predetermined rate;
a sterilizing tunnel containing superheated water at a pressure P1 greater than the pressure that is likely to exist in the packages being sterilized;
a transfer lock in which the pressure P1 subsists, said transfer lock being suitable for receiving carriages from the sterilizing tunnel at said rate;
a cooling tunnel containing cooling water at a pressure P1; and
an outlet lock suitable for receiving carriages coming from the cooling tunnel at said rate, prior to delivering them to the unloading station;
means for maintaining the water in the sterilizing tunnel at the required temperature and at the pressure P1;
means for maintaining the water in the cooling tunnel at the pressure P1;
means for causing the carriages to advance from the loading station to the unloading station;
means for transferring an empty carriage from the unloading station to the loading station; and
means for causing the doors of the locks to open and close synchronously with the means for causing the carriages to advance.
The installation is characterized by the fact that the sterilizing tunnel, the cooling tunnel, and the locks are made of a non-magnetic material, and the means for causing the carriages to advance inside the sterilizing tunnel and the cooling tunnel comprise linear magnetic couplers.
Advantageously, the linear magnetic couplers comprise magnetic receiver circuits mounted on the carriages and magnetic transmitter circuits mounted to move outside the tunnels.
Preferably, the transmitter magnetic circuits are carried by endless belts mounted beneath the tunnels or tunnel segments.
The tunnels and the locks are thus free from any mechanical devices for moving the carriages. This greatly simplifies maintenance of the installation.
In addition, during treatment of the products, i.e. during sterilization and cooling, the packages are subjected to the same pressure P1 greater than the pressure that is liable to exist inside the packages during sterilization. It is only on leaving the outlet lock, once the products are cold, that the packages are subjected to atmospheric pressure.
There is thus no danger of the packages bursting due to excess internal pressure.
To reduce the floor area occupied by the installation, the path through the sterilizing tunnel and the cooling tunnel comprises an even number of superposed path segments, means being provided for transferring carriages vertically from a lower path segment towards the next higher path segment. The unloading station is situated immediately above the loading station. The means for transferring a carriage from a lower segment to a higher segment comprise an elevator device for raising a carriage, and a thrust actuator for transferring the carriage from the elevator device to the beginning of the higher path segment.
It is also preferable to adopt the following advantageous provisions:
the superheated water circulates in the sterilizing tunnel in the opposite direction to the direction in which the carriages advance and is supplied by a water heater device, and is maintained therein at the pressure P1 by the presence of a first hydropneumatic accumulator connected to a source of compressed air and mounted on the sterilizing tunnel; and
the cooling water circulates in the cooling tunnel in a direction opposite to the travel direction of the carriages and is maintained at the pressure P1 therein by the presence of a second hydropneumatic accumulator connected to a source of compressed air and mounted on the cooling tunnel.